Mix Shader Fac doesn't work
Your current screen shot shows you are in Solid draw mode and that will not update to preview your material, change it to Material draw mode and you will get a better idea of what is going on. Even faster idea of what is going on is to set a border in the 3d view with Ctrl-B and to then press Shift-Z to change to Render preview mode inside the border, and that way you will see actual feedback as you change the shader.